A radio frequency identification (RFID) system, becoming widespread in recent years, is used in article management such as inventory management, by affixing an RF tag to a article to be managed.
Examples of such an RFID system are disclosed in PTLs 1 to 4. Technologies described in PTLs 1 to 4 manage a article to be managed by affixing an RF tag to the article to be managed, and, when tag information in the RF tag can be read, determining that the article to be managed is present, and, when the tag information cannot be read, determining that the article to be managed is not present. However, there are following problems in such a use of the RFID system.
First, there is a problem of improper reading of tag information in an RF tag. For example, when the system is used for commodity management on a display shelf at a retail store, a third person other than a consumer having intention to purchase a commodity or a clerk involved in commodity management may read tag information in an RF tag affixed to the commodity. In such a case, there is a problem, for example, that information about the commodity being purchased or has been purchased by the consumer may be associated with the consumer, resulting in invasion of privacy. Further, when a raw material stored in a warehouse or a product to be shipped is similarly managed by the RFID system, there is also an information security problem that a third person may become aware of warehousing/delivery status of the raw material or the product, being attached with an RF tag, by reading tag information in the RF tag.
Secondly, there is a problem that a cost of an RF tag is high. Although a cost of a tag in an ultra-high frequency (UHF) band is currently reduced to lower than ten yen per piece, the cost is about two orders of magnitude higher than a cost of a bar code similarly used in article management, particularly in commodity management. Consequently, it is difficult from a viewpoint of cost to attach an RF tag to an article at roughly 1000 yen or lower.
A technology for dealing with such problems is disclosed in PTL 5. Similarly to the aforementioned RFID system, a technology of performing article management is disclosed in PTL 5. More precisely, PTL 5 is related to a smart shelf using an RFID system, and is related to a technology of monitoring presence or absence of an article on a shelf.
In PTL 5, an RF tag is positioned on a shelf. Then, an article being a managed object (hereinafter referred to as article to be managed) is positioned so that the article blocks read operation of an RFID reader on a plurality of RF tags positioned on the shelf. In other words, in PTL 5, a article to be managed is positioned between an RF tag and an antenna attaching to the RFID reader. Then, in PTL 5, a quantity of articles is monitored through a following procedure.
(a) The RFID reader irradiates an electromagnetic wave on the shelf.
(b) The number of RF tags from which the RFID reader is not able to read tag information due to presence of an article, is measured.
(c) A quantity of articles is measured, in accordance with the information obtained in (b).
An RF tag is adjusted so that an article hinders the reader from reading the tag when the article is positioned between the reader and the tag.
In the technology described in aforementioned PTL 5, when an article to be managed is positioned between the RFID reader and an RF tag, that is, when an article to be managed is present on the shelf, the RFID reader is not able to read tag information in the RF tag, due to the article blocking a line of sight between the RF tag and the RFID reader. In other words, when an article to be managed is present, tag information in the RF tag corresponding to the article cannot be read, and therefore presence of the article to be managed can be detected. By contrast, when an article to be managed is not present on the shelf, that is, when an article to be managed is not present between the RFID reader and an RF tag, an article to be managed blocking a line of sight between the RF tag and the RFID reader is not present, and therefore the RFID reader is able to read tag information in the RF tag. Accordingly, when an article to be managed is not present, tag information corresponding to the article can be read, and therefore absence of the article can be detected. Consequently, in PTL 5, presence or absence of an article can be detected, and article management on the shelf can be performed. It is assumed that a manageable article is an article containing metal, water, or the like, hindering transfer of energy at a radio frequency.
In the technology in aforementioned PTL 5, an RF tag is not affixed to an article to be managed and remains on the shelf, and therefore a problem of invasion of privacy and information security, due to improper reading of tag information in an RF tag affixed to an article to be managed, does not occur. Accordingly, in the technology in PTL 5, the first problem, being a problem of a third person improperly reading tag information in an RF tag, does not occur. Further, in the technology in PTL 5, an RF tag is not affixed to an article and remains on a shelf, and therefore the RF tag can be repeatedly used and a tag cost per article substantially becomes a value of the cost divided by a tag use count. In other words, in the technology in PTL 5, the second problem, being a problem of a high RF tag cost, is solved by sufficiently repeated use.
Further, PTLs 6 to 9 disclose technologies of performing contactless signal transfer by electromagnetic coupling. The technologies enable signal transfer even when both ends of a coupler are physically separated, by one end of the coupler being electromagnetically coupled with the other end, either capacitively or inductively.
Further, PTLs 10 to 12 disclose technologies of stabilizing radio communication when reading an RFID tag. In PTL 10, attenuation of magnetic field current within a resonance circuit is reduced, by passing a magnetic field generated by electromagnetic coupling, through a circular magnetic material layer, thus stabilizing radio communication. PTLs 11 and 12 disclose suppression of mutual interference between neighboring RFID tags, by positioning an interference suppression means.